1. Field of the Invention
The present invention relates to a power converter which includes an inverter circuit for improving an input power factor and converts AC power into DC power.
2. Description of the Related Art
In a conventional power converter, an inverter circuit (single-phase inverter) is connected in series to a rectifying circuit for rectifying an AC input in a subsequent stage of the rectifying circuit; and a smoothing capacitor is connected through a rectifying diode to the inverter circuit in a subsequent stage of the inverter circuit. Further, a short-circuit switch is provided to bypass the smoothing capacitor, and an output of the inverter circuit is controlled based on a current command so that a DC voltage of the smoothing capacitor follows a target voltage and an input power factor is improved (see, for example, JP 2009-095160 A).
However, the conventional technology has the following problems. In the conventional power converter, it is necessary to output, from the inverter circuit, a difference between an AC input voltage and an output voltage of the power converter. Therefore, when the output voltage is to be increased, a turn-on time of the short-circuit switch for charging the inverter circuit lengthens to increase a loss of the short-circuit switch. In addition, a DC voltage of the inverter circuit increases, and hence current control precision reduces and noise increases.
Semiconductor switch elements used in the inverter circuit require large withstanding voltages, and hence there is a problem that losses of the semiconductor switch elements increase.
When the number of single-phase inverters connected in series is increased in order to avoid the problem, a circuit structure and control are complicated. When a current-limiting reactor is increased in size, a large circuit size is required.